False Grunion, Colpichthys regis

False Grunion, Colpichthys regis. Fish caught from coastal waters off Puertecitos, Baja California, July 2012. Length: 7.6 cm (3.0 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).

The False Grunion, Colpichthys regis, is a member of the New World Silverside or Atherinopsidae Family, that is known in Mexico as pejerrey charal. Globally, there are two species in the genus Colpichthys, both are found in Mexican waters of the Pacific Ocean but limited to the northern Sea of Cortez.

The False Grunion has an elongated, deep and strongly compressed body. They are a pale silvery color with a silver stripe along their sides that has a dark line just above. Their head is depressed and broadly flattened dorsally with a straight top profile, a moderately sized eye with a mouth that is partly below the snout with the top jaw being extendible. Their first dorsal fin has 6 spines and originates over the anal fin origin; and their pectoral fins are long. They have 15 to 19 short, compressed, lower gill rakers. They are covered with scales.

The False Grunion is a schooling pelagic species found within coastal lagoons and mangroves areas close to shore at depths up to 4 m (13 feet). They reach a maximum length of 20 cm (7.9 inches). They are active daytime feeders and consume algae and small crustaceans. Reproduction is oviparous. The False Grunion is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The False Grunion is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found only in the northern Sea of Cortez, north of 28°N.

The False Grunion is similar to, and can be confused with the Delta Silverside, Colpichthys hubbsi (translucent green color), the Gulf Grunion, Leuresthes sardina (lack mid-lateral stripe; short pectoral fins), the Jacksmelt, Atherinopsis californiensis (dorsal fins well separated; 30 to 40 lower gill rakers), the Topsmelt, Atherinops affinis (first dorsal fin origin behind anal fin origin; 20 to 35 lower gill rakers).

From a conservation perspective the False Grunion is currently considered to be NEAR THREATENED due to its limited range and the on-going severe habitat destruction, pollution, cessation of flow from the Colorado River, mangrove removal and shrimp aquaculture development. They are rare, small in stature, seldom encountered by humans and of limited interest to most.